Global broadband wireless communications have been growing exponentially in recent years. Network coverage, however, remains incomplete in many regions of the world and even in some currently served regions; thus demand may soon exceed the supply of existing communication infrastructure. Current network technologies are generally too expensive, ineffective, and slow to respond to growing demand. In addition, further proliferation of existing ground-based wireless technologies increases radio-frequency (RF) pollution and human exposure to large amounts of RF energy.
Terrestrial cellular wireless networks are well suited for local area deployments. They are relatively inexpensive, as compared to optical fiber networks, and are the technology of choice in new and emerging markets where the physical infrastructure is limited. Terrestrial cellular wireless networks are appropriate for fixed and mobile users and may be interfaced to wired networks. However, as discrete components, they are range limited and have finite bandwidth. To meet an increasing customer demand, new towers are added to increase the coverage density, while reducing their range to enable increased frequency reuse.
Alternatively, it is possible to establish an aerial network that employs airborne platforms as its main communication hubs. Such hubs would be stationed at altitudes well above commercial airspace, where the line of sight coverage extends over large terrestrial areas. Such a network could work either separately from or together with existing terrestrial mobile phone communication systems. However, one of its potential drawbacks is the limited ability of the airborne antennas to project and concentrate RF emission in small areas on the ground. In wireless cellular communications, where a service area is divided into small cell areas for the purposes of frequency reuse, it is advantageous to be able to project and confine RF emission to these specific small areas, i.e. cell areas. Smaller cell areas allow better frequency reuse and higher throughput per user. The size of the cell area for an airborne antenna is inversely proportional to the antenna's size, so that a larger antenna is more beneficial, since it is capable of producing more concentrated RF emission and smaller cell sizes. Due to the size limitations of a single airborne platform, the size of a single RF antenna may be limited to few meters, which in turn restricts the size of the resulting RF cell area on the ground to no less than several kilometers.
The inventors recognize that this limitation may severely restrict applications of airborne wireless networks. Thus, the inventors believe that there is a strong need for a way to improve the performance of airborne antennas and propose several solutions.